1. Field of the Invention
This disclosure relates generally to a method of forming blown containers, and more particularly to a method of forming blown containers having exterior surface contours.
2. The Prior Art
Prior to the present invention, patterns, grooves, logos or other surface contours have been imparted to the exterior surface of blown thermoplastic containers in the final blow molding step by contours on the interior side walls of the blow mold cavity. Examples of bottles formed in this manner are shown in U.S. Pat. Nos. 3,403,804 and 3,397,724.
This procedure has been generally undesirable because of the expenses involved in machining or otherwise providing the contours on the mold walls and because the contoured molds can only be used for a particular job. Unfortunately, these problems have been heretofore unavoidable since no satisfactory alternative has been available.
The present invention overcomes these problems by applying a desired contour to a parison or preform, particularly of polyethylene terrphthalate material, and then proportionately enlarging that contour as the parison is blown into the final article within a standard blow mold cavity having smooth interior walls.
Of course, parisons and preforms have been provided with contours and varying wall thicknesses prior to the present invention. However, such contours have conventionally been provided either: to achieve an interior reinforcement in the final container, as shown by U.S. Pat. No. 3,114,932; to achieve a visual effect, as shown by U.S. Pat. No. 3,420,924; or to form a reinforced bottle portion, as shown by U.S. Pat. Nos. 3,294,883, 3,137,748 and 3,754,851.
Additionally, the prior art recognizes that polyethylene terephthalate is suitable for forming blown bottles, as shown by U.S. Pat. No. 3,733,309.
In short, however, the prior art does not recognize that profiling may be provided to a thermoplastic preform to achieve exterior contours on a blown container. Additionally, the prior art does not teach that portions of a preform having differential thicknesses may be proportionately reduced in thickness during a blow molding operation.